Non-electrostatic method for producing electrographic image

ABSTRACT

A method for producing an electrographic image from an original provided with a conductivity pattern ranging from a portion having a greater conductivity to a portion having a lesser conductivity, comprising the steps of interposing a thin uniform layer of electrically chargeable particles between a conductive image carrier and said conductivity pattern of said original, said particles having a conductivity lower than that of said image carrier, disposing said original and said conductive image carrier between first and second electrodes so that said original is interposed between said layer of electrically chargeable particles and said second electrode, interposing a dielectric layer between said image carrier and said first electrode to insulate said conductive image carrier therefrom and generating an alternating electric field between said first and second electrodes of sufficient strength so as to charge said electrically chargeable particles whereby said particles receive electric charges having different maximum values according to the different conductivities of said portions of said conductivity pattern whereby the said electrically charged particles are attracted toward and away from said conductivity pattern of said original whereby a portion of said electrically charged particles are removed from said conductivity pattern and form an electrographic image on said image carrier and the remainder of said particles form an electrographic image on said original.

United States Patent [191 Cantarano NON-ELECTROSTATIC METHOD FOR PRODUCING ELECTROGRAPHIC IMAGE [76] Inventor: Marcus Cantarano, 47, Av. F.

Roosevelt-Bat B, Thiais (94),

[21] Appl. No.: 151,489

Related U.S. Application Data [63] Continuation of Ser. No. 631,792, April 18, 1967,

abandoned.

[52] US. Cl 96/1 R, 96/1.4, ll7/l7.5, 317/3, 355/17, 355/17 [51] Int. Cl G03g 17/00 [58] Field of Search ll7/l7.5; 96/1 R, 1.4,

96/15 D, 1 C; 101/45 Y, 457; 118/620, 621, 638, 639, 640; 317/3 [56] References Cited UNITED STATES PATENTS 2,758,524 8/1956 Sugarman 117/17.5 2,758,525 8/1956 Mongrieff-Yeates 117/17.5 2,924,519 2/1960 Bertelson 96/1.4

2,951,443 9/1960 Byrne l17/17.5 2,968,553 l/l96l Gundlach.... 96/l.4 2,976,144 3/1961 Rose ll7/l7.5 3,013,890 12/1961 Bixby ll7/l7.5 3,093,039 6/1963 Rheinfrank..... 1l7/l7.5 3,132,037 5/1964 1l7/17.5 3,132,963 5/1964 ll7/17.5 3,147,147 9/1964 Carlson 1l7/l7.5

3,166,418 1/1965 Gundlach 96/1 R 3,185,051 5/1965 Goffe 96/1.3 3,234,904 2/1966 Van Wagner 118/638 3,247,794 4/1966 Zabiak l17/17.5 3,284,224 ll/1966 Lehmann 117/37 LE 3,326,709 6/1967 Nail 117/l7.5 3,328,193 6/1967 Oliphant et a1. 117/37 LE 3,368,894 2/1958 Matkan et a1 96/1.4 3,427,242 2/1969 Mihajlov 96/1.3 3,585,061 6/1971 Allinger et a1 1l7/l7.5 3,615,383 10/1971 lnoue et a1 117/37 LE 3,721,551 3/1973 Cantarano 96/1 R Primary Examiner-Michael Sofocleous [57] ABSTRACT A method for producing an electrographic image from an original provided with a conductivity pattern ranging from a portion having a greater conductivity to a portion having a lesser conductivity, comprising the steps of interposing a thin uniform layer of electrically chargeable particles between a conductive image carrier and said conductivity pattern of said original, said particles having a conductivity lower than that of said image carrier, disposing said original and said conductive image carrier between first and second electrodes so that said original is interposed between said layer of electrically chargeable particles and said second electrode, interposing a dielectric layer between said image carrier and said first electrode to insulate said conductive image carrier therefrom and generating an alternating electric field between said first and second electrodes of sufficient strength so as to charge said electrically chargeable particles whereby said particles receive electric charges having different maximum values according to the different conductivities of said portions of said conductivity pattern whereby the said electrically charged particles are attracted toward and away from said conductivity pattern of said original whereby a portion of said electrically charged particles are removed from said conductivity pattern and form an electrographic image on said image carrier and the remainder of said particles form an electrographic image on said original.

6 Claims, 6 Drawing Figures NON-ELECTROSTATIC METHOD FOR PRODUCING ELECTROGRAPHIC IMAGE This application is a continuation of my application Ser. No. 631,792, filed Apr. 18, 1967 and now abandoned.

This invention relates to improved methods and means for producing electrographic images.

It is known in the art to develop an electrographic image with a powdered or liquid developer agent by using a latent electrostatic image. This latent image consists in a pattern of electric charges usually generated on the insulating indicia of a previously prepared printing block, the term printing being intended to denote the orientation of the developer agent in an electric field. The electrographic image is developed by electrically orienting a developer agent in conformity with the indicia of the printing block. The developed image may be obtained on the printing block and thus act as an image carrier. In addition, an electrographic image may be developed on a second image carrier that is in the form of a sheet carrying a layer of developer powder, this coated sheet being placed against the latent electrostatic image of the printing block to orient the powder thereby developing the visible image.

The printing block may be of a different nature although it is usually constituted by a photoconductive layer onto which the latent electrostatic image is produced with the aid of optical means by radiation. The use of such a latent electrostatic image, however, limits the working speed of the process and often requires the use of complicated devices. These disadvantages become particularly important where a liquid developer is used. Nevertheless, even when a powder is used, the carrying out of existing methods necessitates the insulating character of the indicia of the printing block in order to maintain the latent electrostatic image during the development of the visible image. Hence the working of actual electrography is limited by the use ofa few specially prepared printing blocks and in particular by the use essentially of only a few photoconductive insulating materials.

Now in accordance with the instant invention an electrographic image may be formed and simultaneously developed without producing a latent electrostatic image on a particular insulating printing block. The developed image may now be produced by using any kind of printing block provided with a surface including at least an indicia area having an electric conductivity different from that of the remaining area of said surface. Such a surface original is termed a conductivity pattern." Accordingly, in addition to the usual printing blocks, traces of conductive inks, letterpress printing, photographs and any other conductivity pattern may also be used to produce developed images according to this invention. In the following specification the term original" is intended to denote any backing support carrying on its surface a conductivity pattern adapted to the production of electrographic images.

In its simplest form, the present invention pertains to the production of electrographic images from a thin uniform layer of developer powder placed in contact with the conductivity pattern of an original. An electric field is generated across the powder to orient and distribute it in accordance with the indicia of the original and thus to produce and simultaneously develop an electrographic image. A developed image may be obtained on the original and eventually on an image carrier sheet which is placed against the layer of developer powder during the application of the electric field. A copy may be obtained by fixing the developed image on the original or on the image carrier. In addition, the electrographic image may be transferred from the original and from the image carrier onto support materials to provide copies of the original in upright form.

More specifically, according to a first embodiment of the present invention a thin uniform layer of developer powder is interposed between an image carrier and the conductivity pattern of an original; the original and the image carrier are interposed between two electrodes with the original electrically insulated from its adjacent electrode; an electric field is generated between the electrodes to orient the powder in conformity with the pattern on the original; and either the image carrier or the original is used for producing a copy after the image carrier is separated from the original.

In carrying out the present invention an insulating, as well as a conductive, image carrier may be used. If a conductive image carrier is used, a dielectric layer may be interposed between the image carrier and its adjacent electrode to advantageously insulate the image carrier from the electrode.

According to another embodiment of the present invention an image carrier is used with an electrical conductivity which is between the maximum and the minimum conductivities of the conductivity pattern of the original. For example, where the indicia of said pattern have a high electrical conductivity and the remaining pattern has a low electrical conductivity, the image carrier will have an electrical conductivity greater than said low conductive areas of the original but lower than the indicia. According to this embodiment a thin uniform layer of powder is sandwiched between said image carrier and the conductivity pattern of the original, and an electric field is generated between two electrodes to electrically orient the powder in conformity with the conductivity pattern of the original.

Similar to the aforementioned first embodiment of the invention, the original or alternatively the image carrier, or both, may be insulated from their respective adjacent electrodes.

When the image carrier is separated from the original, the developer powder forms a first electrographic image on the original and a second one on the image carrier. The two images constitute, respectively, a positive and a negative image of the conductivity pattern of the original.

Alternatively, said first or second electrographic image may be transferred onto a copy material by repeating the aforedescribed method of the invention.

For example, the powder of the images may be fixd on the copy material by means of a fixing varnish or, if fusible powders are used, by heat fusing the powder.

On the other hand, when only one electrographic image is to be produced on the surface of the original, instead of said image carrier, a dielectric fluid layer of air may be interposed between the conductivity pattern of the original and its facing electrode, the latter being advantageously shaped in the form of a grid.

Although said electric field may be generated for producing developed images, it is particularly advantageous to alternatively change the direction of the electric field for developing electrographic images in accordance with the instant invention. 9

An appropriate apparatus for practicing the method includes two electrodes connected to a voltage source. One of the electrodes may take the form of a rotatable drum. The original is placed between the drum and a second electrode, and the image thereby formed on either the original or the drum is subsequently transferred to a copy paper.

An object of this invention is to improve electrographic methods and to provide devices and apparatus for use in electrography.

Other objects of this invention will be apparent from the following description and accompanying drawing taken in connection with the appended claims.

Several embodiments of the invention will now be described by way of example and with reference to the accompanying drawing, in which:

FIG. 1 is a diagrammatic sectional view of an electrographic arrangement showing an original with a conductivity pattern thereon and a sheet serving as an image carrier, with the sheet and original disposed between two electrodes;

FIG. 2 is a schematic representation of the electric charges on particles between the original and the image carrier;

FIG. 3 is a second schematic representation of the electric charges on particles between the original and the image carrier;

FIG. 4 is a schematic representation of an arrangement showing an original disposed between a first gridshaped electrode and a second electrode;

FIG. 5 is a diagrammatic representation in side elevation of an electrographic copying device having a drum shaped electrode; and

FIG. 6 is a diagrammatic view in side elevation of another embodiment of an electrographic copying device in which the original is carried by a drum.

In the arrangement shown in FIGS. I to 3, for producing an electrographic image, an original provided with indicia 2 having an electric conductivity other than the surface 3 of the conductivity pattern 2, 3 of the original is disposed between two electrodes 6 and 7. Also arranged between the electrode 6 and 7 is an image carrier 4 coated with a uniformly distributed powder 5 on its surface facing the conductivity pattern 2, 3.

Where the original is provided with a conductive backing material 1, a dielectric 8 may be disposed between the backing l and electrode 7. If the image carrier 4 is made of a conductive material, a dielectric layer may be interposed between the image carrier 4 and electrode 6. The electrodes 6 and 7 are provided with terminals 9 and 10, respectively.

Any kind of original may be used in the device of FIGS. I to 4. According to embodiments of the invention, if a specially prepared printing block is used as an original, it is not used as an electrode. Rather, the conductive areas of the pattern 2, 3 are separated from the electrode 7 by the interposition of the dielectric 8 (FIG. 1), or alternatively by the backing material 1 (FIG. 4) when the latter is made of an insulating material.

More generally, in carrying out the instant invention, an original may be used which is provided with an electrically conductive or an insulating material and the indicia may consist of an electrically conductive or insulating material. The indicia need not even be visible as are, for example, graphic records. In this conjunction it is also essential to note that between the maximum and the minimum conductivities of the pattern 2, 3, intermediate conductivities may be found, it being also possible that the conductivity of either the indicia 2 or the surface 3 is equal to zero. Accordingly, when sharpcontrast and very accurate reproduction of the halftone (gray-tone values) of the image is to be achieved, a further embodiment of the invention utilizes a conductivity pattern 2, 3 provided with said intermediate conductivities together with the use of an image carrier having a uniform electrical conductivity between the maximum and the minimum conductivities of the pattern 2, 3 of the original.

According to another embodiment of the invention, a metallic conductive image carrier 4 is used, as for example a sheet of steel or aluminium. In this case the sheet 4 is preferably coated with a loosely sticky layer of, for example, zinc stearate, in order to coat said metallic image carrier 4 with a loosely-adhering layer of developer powder. In this embodiment, due to the presence of the metallic sheet 4, the electric resistance between the electrodes 6 and 7 is diminished, and thus a dielectric layer 8 is interposed preferably between the backing I of the original and electrode 7. This arrangement avoids a useless intense electric current through the device. The dielectric 8 consists, for example, of a sheet of mylar (registered trade mark) of a thickness of 150 microns.

Instead of coating the powder 5 onto the surface of the image carrier 4, according to the above described method, the powder can, alternatively, be coated onto the surface of the original so that a thin uniform layer coats the entire conductivity pattern 2, 3. Such a coating of the powder onto either the image carrier 4 or the original can be accomplished in a well known manner by the use of rotating brushes, by spraying or cascading the powder.

Referring to FIGS. 1 to 4, an high voltage may be applied to the terminals 9 and 110 of the electrodes 6 and 7. For example, a direct voltage of the order of 25 KV may be applied to the terminals for a period of a fraction of I second although, the satisfactory quality of the electrographic image is independent of a longer duration of the developing electric field. The voltage may be alternatively applied for a period of one second, for example. However, the best quality of the developed image is obtained if an alternating voltage is applied to the terminals 9 and 10. For example, alternating voltages of5 KV.5O cycles/sec, 3,5 KV.250 cycles/sec may be applied. Instead of this, it is also possible to apply to terminals 9 and 10 an impulsion of attenuated or an oscillating modulated voltage.

When, subsequently, the electrodes 6 and 7 (FIG. 1) are separated and the image carrier 4 is detached from the original, the powder 5 is distributed according to the indicia 2 both on the original and on the image carrier 4 and in this distributed form it may be used for producing a copy. During the image development an external pressure, for example, of about g/cm may be exerted on the electrodes 6 and 7.

The manner in which the powder 5 is distributed on the image carrier 4, as well as on the surface 2, 3 of the original, depends upon the electrical properties of the powder 5. An electrically insulating powder is attracted to the several surfaces in a manner different from an electrically conductive powder.

FIG. 2 shows two grains 5' and 5" of a powder which is electrically insulating, the grains 5 and 5" being disposed between the image carrier 4 and the conductivity pattern 2, 3 of the original. It will be appreciated however that the powder is in the form of a layer and that numerous particles will form the thickness of the layer of powder. For example, an original may be used in which the electrical conductivity of the indicia 2 is greater than the conductivity of the areas 3. Under the action ofa very intense electric field across the original 1 and the image carrier 4, the greater mobility of the electric charges in the better electrical conductor provides a higher concentration of charges in the grains of powder 5 against the indicia 2. Consequently, when the original is separated from the image carrier 4 after the application of the electric field, the grains of the insulating powder 5 opposite the more conductive indicia 2 will be attracted away from the image carrier 4, as shown by the arrow for the particles 5, and the insulating powder 5 opposite the less conductive areas 3 remains applied on the image carrier 4, as shown by the arrow for the particle 5". It may be stated that the grains of an insulating powder will be more strongly attracted towards the better electric conductive area of the conductivity pattern 2, 3. It will thereafter be appreciated that, by using an original having more conductive areas 3 and less conductive indicia 2, the grains of insulating powder 5 will move opposite to the directions of the arrows of FIG. 2.

FIG. 3 shows two grains 30' and 30" of an electrically conductive powder 5 which are placed against the indicia 2 and the surface 3 of an original, respectively. Where the electric conductivity of the indicia 2 is greater than the conductivity of the surface 3, under the action of a preferably alternating electric field between the electrodes 6 and 7, the grains of the conductive powder 5 opposite to the less conductive surface 3 will electrically overcome their adherence to the image carrier 4 and they will be attracted toward the surface 3, as shown by arrow for the particles 30". At the same time, the grains of the conductive powder 5 opposite to the more conductive indicia 2 remain on the coated image carrier 4, as shown by the arrow for the particles 30'. By using an original provided with surfaces 3 having a conductivity greater than that of indicia 2, the particles of powder 5 move opposite to the directions shown by the arrows in FIG. 3. Hence, it may be stated that a conductive powder 5 is more strongly attracted towards the less conductive parts of the pattern 2, 3 of the original. In carrying out the present invention it is expedient to use an image carrier having an electrical conductivity between the maximum and the minimum conductivities of the pattern 2, 3 of the original. Such an image carrier may be in the form of a sheet, as for example a sheet of conductive paper. As shown in FIG. 3, an original may be used which is provided with indicia 2 having an electrical conductivity higher than that of the surface 3. In this example, the electric conductivity of the image carrier 4 is higher than the electric conductivity of the surface 3. The conductivity of the indicia 2 is higher than the electric conductivity of the image carrier 4. By virtue of these relative conductivities of the indicia 2, surface 3 and sheet 4, the contact conductance between the grains 30" and the surface 3 is lower than the contact conductance between the grains 30" and the image carrier 4. Similarly, the contact conductance between the grains 30 and the image carrier 4 is lower than the contact conductance between the grains 30' and the indicia 2. When a voltage is applied to the terminals 9 and 10 so that electrodes 6 and 7 create an electric field, each grain of the powder 5 is electrically charged to the polarity of that surface to which the contact conductance is higher and will be attracted to the other surface to which it has a lower contact conductance. Hence it may be stated that an electrically conductive powder will migrate from the surface of higher electrical conductivity to the surface of lower conductivity. This effect depends only on the relative conductivities of the indicia 2, the surface 3 and image carrier 4. The development of the image is independent of the direction of the electric field, of a critical duration of the field and of a particular conductivity of the areas 2 and 3 of the original. Advantageously, an alternating field may be generated between electrodes 6 and 7 to develop electrographic images by the device of FIG. 1, and particularly sharp contrast and a very accurate reproduction of the half-tones (gray tone values) are achieved by using said image carrier having an electrical conductivity between the electric conductivity of areas 3 and that of the indicia 2.

After separating the original 1 from the image carrier 4, a reversed or mirror-like image of the indicia 2 will be formed on the image carrier 4. At the same time that the reversed image is formed on the image carrier 4, a non-reversed or upright image develops on the original. These reversed or alternatively upright images are termed positive if the half-tone scale of the indicia is retained unchanged, so that the areas with powder on the developed image correspond to the indicia of the original, and the clean areas of the powder image correspond to the areas 3 of the original. On the other hand, the electrographic image is termed negative" if its areas with powder correspond to the areas 3 of the original, and the clean areas correspond to the indicia 2.

Where the original to be reproduced is provided with indicia 2 having an electrical conductivity higher than that of the surface 3, by using a conductive powder a positive reversed image is formed on the image carrier 4 and a negative upright image on the original. By using an insulating powder, a negative reversed image is formed on the image carrier 4 and a positive upright on the original. On the other hand, when the original is provided with indicia 2 having an electrical conductivity lower than that of the surface 3, by using an insulating powder a positive reversed image is formed on the image carrier 4 and a negative upright image on the original 2, 3; by using a conductive powder, a negative reversed image is formed on the image carrier 4 and a positive upright on the original.

After the positive or alternatively negative reversed image is formed on the image carrier 4 by using a conductive powder, this image can be transferred, for example, to a sheet of copy paper in order to obtain an upright image. Such transfer may be effected by known methods. Alternatively, it is expedient to develop said image on a metallic image carrier 4 and to effect the transfer of the image onto the copy paper by using the apparatus described below with reference to the FIG.

After separating the image carrier 4 from the copy sheet, the powder which forms the image on the copy paper need only to be fixed to obtain the desired permanent copy. The powder may be fixed, for example, by spraying a fixing varnish onto the powder on the copy, or, if the powder used is a synthetic resin having a low melting point, it is sufficient to heat the copy paper to melt the powder so that the powder adheres to the paper. Such heating may be advantageously accomplished by infra-red radiation.

FIG. 4 shows another embodiment of a device for producing electrographic images in which a powder coated original having a backing l and a conductivity pattern 2, 3 is disposed under an electrode in the form of a grid 11. A second electrode 7 is disposed beneath backing 1. In this embodiment the indicia 2 is electrically insulated from the electrode 7 by forming backing 1 from an electrically insulating material. Alternatively, if the backing l is of electrically conductive material, an insulating material is disposed between the backing 1 and the electrode 7. The conductivity pattern 2, 3 and the coating powder 5 are electrically insulated from the grid 11 by a dielectric fluid such as the air layer 4 in the space between grid 11 and the powder 5. The spacing between the grid 11 and the backing l is not critical although it depends on the voltage applied to the terminals 9 and 10 so that, by applying the above mentioned voltages between 25 KV and 3.5 KV, the thickness of the layer 4' is advantageously of about mm.

When a voltage source is connected to the terminals 9 and 10 an electric field is created between electrode 7 and grid 11. Because of this field the electrically conductive powder 5 becomes charged. The coated conductivity pattern 2, 3 being insulated from the electrodes 7 and 11, the different portions of the layer of powder 5 receive electric charges depending only on the different electric conductivities of the corresponding portions of the pattern 2, 3. Hence the differently charged grains of powder 5 are urged toward the grid 11 by different electrical forces which depend only on the conductivities of the pattern 2, 3. Accordingly, where this force is smaller than the adherence of the grain to the original, the grain remains on the original no matter what the duration of the electric field is. A grain above an electrically low conductive spot of the original is urged toward the grid 11 by an electric force smaller than its adherence to the pattern 2, 3 and it remains stably thereon. On the other hand if the grain is above an electrically conducting spot of the pattern 2, 3, the grain is highly charged and it is acted on by an electric force which overcomes the adherence of the grain to the original, and therefore this grain is attracted away from the conductivity pattern 2, 3 through the layer 4 and the grid 11. Hence grains of powder 5 are electrically removed away from the more conductive spots of the original and the powder on the lower conductive areas of the pattern 2, 3 remains stably thereon developing an electrographic image. It will be appreciated that the removed grains of powder are electrically charged from the pattern 2, 3, and consequently this removed part of the powder leaves on the original opposite electric charges tending to annul the existing electric field. In this conjunction it has been found expedient to alternatively change the direction of the electric field between the electrodes 7 and 11. The quality of the obtained images may also be improved by providing the electrode 7 in the form of a bar or wires so that the lines of force of the electric field strongly converge toward electrode 7, this convergence having the effect of improving the adherence of the powder image onto the original during the application of the alternatively modulated electric field.

In the embodiment of FIG. 4, the best results are obtained where the indicia 2 are electrically conductive and the backing material 1 is electrically insulating. In addition, an insulating material may be disposed between the backing I and electrode 7.

For carrying out the method of the invention an apparatus illustrated in FIG. 5 may be used. This apparatus serves to reproduce originals of any kind on any type of paper by developing the electrographic image on a metallic image carrier and to transfer the obtained image onto the copy paper. Hence, the apparatus comprises, preferably, a metallic rotatable drum 12, which functions both as the electrode 6 and the metallic image carrier of the FIG. 1 embodiment. A spraying device 13 including a rotatable brush 14 is arranged for spraying powder through a grid 15 to uniformly coat the surface of the rotating drum 12 with the powder. Thereby a potential difference may be produced between the spraying device 13 and the rotatable drum 12. In operation, the original 1 is continuously driven by an endless belt 17 guided over two cylindrical rollers 16. The original 1 is thus placed against the powder layer on the rotating drum 12. The endless belt 17 is made of an insulating material. Arranged between the two rollers 16 and adjacent to the endless belt 17 is an electrode 18 which functions as the electrode 7 of FIG. 1. The original 1 will travel upwardly out of the apparatus, as shown in FIG. 5.

The voltage applied to the rotatable drum 12 and the electrode 18 is so chosen as to realize the conditions heretofore described with reference to FIGS. 1 to 3. For example, where an original is used which is provided with conductive indicia 2 and low conductive surfaces 3, a conductive powder 5 will be attracted by the surfaces 3 and then brushed off, whereas in the areas that correspond to the indicia 2 the rotating drum 12 will carry along the powder and thus present a positive reversed image.

As shown in the right-hand part of FIG. 5, the apparatus comprises a second pair of rollers 19 guiding an endless belt of dielectric material which is similar to the endless belt 17. The belt 20 is likewise adapted to be placed against the drum 12 by the rollers 19 and an electrode 21 is similarly arranged between the rollers 16 and adjacent to the endless belt 20. The two rollers 19, moreover, serve to guide a web of paper 22 which is unwound from a supply roller 23. The paper 22 will travel as shown by the arrow in FIG. 5. Similarly, at the left-hand part of the apparatus, the electrodes 2l serves to create an electric field between the drum-electrode l2 and electrode 21, this field charging the conductive powder of the image from the metallic drum 12 and thereby electrically transferring this powder onto the paper 22 while the belt 20 urges the paper 22 against the drum 12. An upright positive image is thus produced on the sheet of paper 22. At the outlet of the apparatus this upright positive image will be fixed, for example, by an atomizer 24 adapted to spray an appropriate solvent onto the web of paper 22. The copy of the conductivity pattern of the original will then be obtained at 25 after drying paper 22.

This apparatus can be used for reproducing any kind of original. In particular, commercial originals carrying indicia of pencil traces, drawing ink, letter-press printing as well as photographs and other reproductions may be used.

The embodiment of FIG. 6 serves to produce copies not requiring the separate steps of first developing the image and then transferring it to the copy material. An original is secured to the periphery of a rotatable drum 112. Similar to the FIG. embodiment, a spraying device 113 is arranged for uniformly distributing the powder on the surface of the original. When the drum 112 is rotating, the powder coated original passes below the grid 111 which functions in a manner essentially the same as the grid 11 of FIG. 4. It will however be appreciated that in the arrangement of FIG. 6 the grid 111, the layer of powder 5 and the original 2, 3 are disposed parallel to a vertical plane on the periphery of the drum 112. When a voltage is applied between the rotatable drum 112 and the grid 111, which is equivalent to the grid 11 of FIG. 4, the powder 5 is electrically removed from the conductive parts of the conductivity pattern 2, 3, leaving an electrographic image on the less conductive parts of the conductivity pattern of the original on the rotatable drum 112.

In the arrangement at the right-hand part of FIG. 6, the pair of rollers 119 and the endless belt 120 correspond in FIG. 5 to the rollers 19 and the belt 20, respectively. This arrangement serves to effect the trans fer of the image from the original 2, 3 to the web of paper 122 while the latter is continuously placed against the rotating drum 112 so that an upright image is produced on the web of paper 122. At the outlet of the apparatus this upright image will be fixed by an atomizer I24 adapted to spray an appropriate solvent onto the web of paper 122.

Another embodiment of the apparatus shown in FIG. 5 consists in the arrangement where the original is secured to the rotatable drum 12. An intermediate image carrier may be used as the original, whereby a first negative reversed copy is first formed on a sheet of paper by the method described above with reference to FIG. 5, and then the thus prepared image bearing sheet of paper is secured to the periphery of the drum 12 as an original. A second spraying device is arranged on the upstream side of the two rollers 19 so that two electrographic images will be formed on each revolution of the drum 12. One of the two images is produced on the web of copy paper driven by the rollers 12 and the other one is produced under the rollers 16 which are likewise associated with identical supply rollers 23 and a second atomizer 24. It will be appreciated that, by using this embodiment of FIG. 5, each one of the two electrographic images is produced and simultaneously transferred onto its corresponding copy paper.

For the arrangement of FIG. 1 to function properly, the powder 5 must not have an extremely high electrical conductivity. If the powder 5 is too highly electrically conductive, a sufficient number of grains of powder may move to the low conductive parts of the pattern 2, 3 to form an electrically conducting layer with a conductivity similar to the whole surface 2, 3 of the original. If this occurs, there will be essentially no differences in the electric conductivity of the areas 2, 3 on the original. Correspondingly, the proper image will not be formed on the image carrier 4.

However, by selecting powder 5 such that the electrical contact conductance between the individual grains of the powder is equal or lower than the contact conductance between the grains of the powder and the image carrier 4, the conductivity differences on the pattern 2, 3 do not disappear when the grains are attracted to and cover the low conductive areas of the pattern of the original. Hence, a good electrographic image is formed. Thus, in the device of FIG. 1 it is expedient to use a developer powder 5 having an electric conductivity lower than that of the image carrier 4. If, however, a metal image carrier is used, a metallic pow der may be used, for example a powder having an electric resistivity between 4,000 and 15,000 ohm/cm. In addition, when an oxidized metallic powder presents a black hue, such oxidized metallic powder may be used. The developer powder is preferably passed through a sieve having for example a mesh width of about 50 microns. The powder thus obtained may be rendered loosely-sticky by coating it for example with stearic acid or stearate so that this powder may be used to be applied to the drum of the apparatus of FIGS. 6 and 7. When a metallic image carrier is used as described with reference to the FIG. 1 embodiment, the metallic image carrier may also be similarly coated to hold the powder layer 5.

In addition, a developer other than a powder may be used as for example a liquid and then the apparatus may be constructed also in such a manner that when an original or, alternatively, an image carrier is coated with the developer and simultaneously advanced, the

coated original travels with the image carrier in a straight way. This arrangement avoids centrifuging off portions of the powder or liquid respectively.

While the methods herein described, and the apparatus for carrying out these methods constitute preferred embodiments of the invention, it is to be understood that the invention is not limited by these precise methods and apparatus, and changes may be made in either without departing from the scope of the invention which is defined in the appended claims.

Having thus set forth and disclosed the nature of this invention, what is claimed is:

l. A method for producing an electrographic image from an original provided with a conductivity pattern ranging from a portion having a greater conductivity to a portion having a lesser conductivity comprising the steps of:

a. interposing a thin uniform layer of electrically chargeable particles between a conductive image carrier and said conductivity pattern of said original,

b. disposing said original and said conductive image carrier between a first and a second electrode so that said original is interposed between said layer of electrically chargeable particles and said second electrode,

0. interposing a dielectric layer between said image carrier and said first electrode to insulate said conductive image carrier therefrom and d. generating an alternating electric field of sufficient strength between said electrodes to charge said electrically chargeable particles whereby said particles receive electric charges having different maximum values according to the different conductivities of said portions of said conductivity pattern whereby the said electrically charged particles are attracted toward and away from said conductivity pattern of said original whereby a portion of said electrically charged particles are removed from said conductivity pattern and form an electrographic image on said image carrier and the remainder of said particles form an electrographic image on said original.

2. The method of claim 1 wherein said conductive image carrier has a conductivity intermediate the portion of said conductivity pattern having said greater conductivity and the portion of said conductivity pattern having said lesser conductivity.

3. The method of claim 1 wherein said original is provided with a conductive backing material and which includes interposing an insulating layer between the conductive backing material and said second electrode.

4. The method of claim 1 wherein said original is provided with an insulating backing material and said second electrode is in the form of wires.

5. A method for producing an electrographic image from an original provided with a conductivity pattern ranging from a portion having a greater conductivity to a portion having a lesser conductivity, said conductivity pattern being affixed to a conductive backing material, comprising the steps of:

a. coating said conductivity pattern with a thin layer of electrically chargeable particles,

b. disposing said original and a fluid insulating layer between a grid-shaped first electrode and a second electrode so that said layer of electrically chargeable particles is interposed between said conductivity pattern and said grid-shaped first electrode,

c. generating an alternating electric field between said electrodes of sufficient strength to charge said electrically chargeable particles whereby said particles receive electric charges having different maximum values according to the different conductivities of said portions of said conductivity pattern whereby the said electrically charged particles are attracted toward and away from said conductivity pattern on said original whereby a portion of said electrically charged particles are removed and an electrographic image is formed on said conductivity pattern from the remaining electrically charged particles and said portion of electrically charged particles removed from said conductivity pattern is attracted through said fluid layer and said gridelectrode away from said electric field.

6. The method of claim 5 wherein an insulating layer is interposed between said conductive backing material and said second electrode. 

1. A METHOD FOR PRODUCING AN ELECTROGRAPHIC IMAGE FROM AN ORIGINAL PROVIDED WITH A CONDUCTIVITY PATTERN RANGING FROM A PORTION HAVING A GREATER CONDUCTIVITY TO A PORTION HAVING A LESSER CONDUCTIVITY COMPRISING THE STEPS OF: A. INTERPOSING A THIN UNIFORM LAYER OF ELECTRICALLY CHARGEABLE PARTICLES BETWEEN A CONDUCTIVE IMAGE CARRIER AND SAID CONDUCTIVITY PATTERN OF SAID ORIGINAL, B. DISPOSING SAID ORIGINAL AND SAID CONDUCTIVE IMAGE CARRIER BETWEEN A FIRST AND A SECOND ELECTRODE SO THAT SAID ORIGINAL IS INTERPOSED BETWEEN SAID LAYER OF ELECTRICALLY CHARGEABLE PARTICLES AND SAID SECOND ELECTRODE, C. INTERPOSING A DIELECTRIC LAYER BETWEEN SAID IMAGE CARRIER AND SAID FIRST ELECTRODE TO INSULATE SAID CONDUCTIVE IMAGE CARRIER THEREFROM AND D. GENERATING AN ALTERNATING ELECTRIC FIELD OF SUFFICIENT STRENGTH BETWEEN SAID ELECTRODES TO CHARGE SAID ELECTRICALLY CHARGEABLE PARTICLES WHEREBY SAID PARTICLES RECEIVE ELECTRIC CHARGES HAVING DIFFERENT MAXIMUM VALUES ACCORDING TO THE DIFFERENT CONDUCTIVITIES OF SAID PORTIONS OF SAID CONDUCTIVITY PATTERN WHEREBY THE SAID ELECTRICALLY CHARGED PARTICLES ARE ATTRACTED TOWARD AND AWAY FROM SAID CONDUCTIVITY PATTERN OF SAID ORIGINAL WHEREBY A PORTION OF SAID ELECTRICALLY CHARGED PARTICLES ARE REMOVED FROM SAID CONDUCTIVITY PATTERN AND FORM AN ELECTROGRAPHIC IMAGE ON SAID IMAGE CARRIER AND THE REMAINDER OF SAID PARTICLES FORM AN ELECTROGRAPHIC IMGE ON SAID ORIGINAL.
 2. The method of claim 1 wherein said conductive image carrier has a conductivity intermediate the portion of said conductivity pattern having said greater conductivity and the portion of said conductivity pattern having said lesser conductivity.
 3. The method of claim 1 wherein said original is provided with a conductive backing material and which includes interposing an insulating layer between the conductive backing material and said second electrode.
 4. The method of claim 1 wherein said original is provided with an insulating backing material and said second electrode is in the form of wires.
 5. A method for producing an electrographic image from an original provided with a conductivity pattern ranging from a portion having a greater conductivity to a portion having a lesser conductivity, said conductivity pattern being affixed to a conductive backing material, comprising the steps of: a. coating said conductivity pattern with a thin layer of electrically chargeable particles, b. disposing said original and a fluid insulating layer between a grid-shaped first electrode and a second electrode so that said layer of electrically chargeable particles is interposed between said conductivity pattern and said grid-shaped first electrode, c. generating an alternating electric field between said electrodes of sufficient strength to charge said electrically chargeable particles whereby said particles receive electric charges having different maximum values according to the different conductivities of said portions of said conductivity pattern whereby the said electrically charged particles are attracted toward and away from said conductivity pattern on said original whereby a portion of said electrically charged particles are removed and an electrographic image is formed on said conductivity pattern from the remaining electrically charged particles and said portion of electrically charged particles removed from said conductivity pattern is attracted through said fluid layer and said grid-electrode away from said electric field.
 6. The method of claim 5 wherein an insulAting layer is interposed between said conductive backing material and said second electrode. 